Infusion systems for the infusion of liquid therapeutic products into the human or animal body are known in the art, e.g. from U.S. Pat. No. 4,395,259. Such systems are particularly, though not exclusively, intended for the infusion of insulin into the body for diabetes therapy. The system has an infusion device which may be implanted or worn externally on the body, and a remote controller that can wirelessly monitor the function of the infusion device. The infusion device includes a pump (typically a micro-pump) connected to an infusion set, a reservoir of the therapeutic product, control electronics and a battery power supply. The infusion set includes a cannula attached subcutaneously to the patient's skin.
When the infusion device is first assembled, air is likely to be present within the various cavities of the device. The air is required to be evacuated during the first filling and priming of the device ready for use, since any air remaining will form air bubbles within the pumping chamber, which may otherwise lead to under dosing.